DEMONSTRATION.(3 HRS)Introduce the students in groups of no morethan 5 to the engine that they will be using during the disassemblyand reassembly process.The engine starter and 2 12 volt batterieswill be required.

Will demonstrate with one group at a time. Allother groups

will be in the classroom with study material.

STUDENT ROLE:The students will become familiar with and see how tostart their engine. They should also ask any questions at this time.

INSTRUCTOR ROLE:

Demonstrate how to correctly run the engines forthe students.

1.1st

step-

Have students get two 12v batteries, fuel can with fuelfrom hazmat

and the starting switch from the tool room.

2.2nd

step-

Have students ensure that all engine radiators

are fullprior to starting the engine.

3.3rd

step-

Hook

batteries and start switch to engine. Start engine.

1. Safety Brief:

Make sure students know how to hook up thebatteries correctly. At all times

proper PPE will be worn. Make sureto stay clear of the fan and all hot components.

Exhaust fan shouldbeon at all times that the engine is running.

2. Supervision and Guidance:

The instructor will hook up the enginestart switch to the starter and hook up the two 12 volt batteries tothe starter also. Start engine and show the students that it runsprior to their disassembly.

3. Debrief:

(If applicable)(Allow students the opportunity tocomment on what they experienced and/or observed. Provide overallfeedback, guidance on any misconceptions, and review the learning

points of the demonstration.

INSTRUCTOR NOTE

Perform the Following demonstration.

QUESTIONS FROM THE CLASS:

QUESTIONS TO THE CLASS:

Q:Describe three characteristics unique to a Diesel Engine.

A: Uses compression to generate heat used to ignite fuel air mixture,has high compression ratio and is built out of heavy materials towithstand the high compression.

Q: In which type of combustion chamber design has the combustionchamber formed in the piston head?

A: Open Chamber

Q: Describe four ADVANTAGES of a Diesel Engine.

A: More efficient than most other engines, requires no-ignition tuneup, diesel fuel is less volatile, and they produce tremendous low-speed power.

Q:Define the term Power Overlap.

A: Before one power stroke ends, another one begins.

Q: Define the term mechanical efficiency.

A: The relationship between the power

produced in the engine and theactual power delivered at the crankshaft.

Q: The force that tends to result in the twisting of the objectrather than its physical movement.

A: Torque

Q: What is method that is used to measure how tightly the mixture issqueezed during the compression stroke?

A: Compression Ratio

TRANSITION:Any more questions? If not let’s move ontodiesel engineintake and exhaust systems.

The earth is surrounded by an ocean ofair that is known as the atmosphere. Because it is colorless andodorless, people are not always aware of it. However, the atmospheredoes have weight.

(2)Atmospheric Pressure.

Elevation is always referred toin relation to the level of the ocean. This is known as sea level.Because the atmosphere extends for many miles above the earth, theweight of all of this air creates a large force on the earth’ssurface. In fact, the weight of the air creates a pressure ofapproximately 14.7 PSI or 1 Bar on all things at sea level. As theelevation increases, this atmospheric pressure progressivelydecreases.

(ON SLIDE #128)

(3)Vacuum in the Cylinder.

When the piston moves downwardon

the intake stroke, it may appear that it is sucking the mixtureinto the cylinder. Actually, what is really happening is that by thepiston moving downward, it is making a larger space in the cylinderthat contains nothing (a vacuum). Theatmospheric pressure outsidethe cylinder will then push its way in through the intake port,filling the cylinder.

QUIZ

(30min)

Hand out quiz for

diesel engine principles of operation.Give the students 20 minutes to complete and reviewit with the students after.

INSTRUCTOR NOTE

Hello Kitty

(ON SLIDE #129)

(4)

Volumetric Efficiency.

(a)

General.

Volumetric efficiency is a way ofmeasuring an engine’s ability to take in, or aspirate, its intake. Asthe piston moves down on the intake stroke, atmospheric pressure willpush the intake into the cylinder. Theoretically, the volume of airthat enters the engine for each intake stroke would be exactly equalto the displacement of the cylinder engine type directly affects howwell this actually occurs.

(ON SLIDE #130)

Diesel engines breathe well because they are un-throttled. The speedof the engine is

proportional to the amount of fuel injected unlikethe gasoline engine in which the speed of the engine is proportionalto the fuel–

air mixture that enters the cylinder. Diesel enginesalways take in more air than what is required for combustion. Sinceall that is needed is more fuel, it is easy to understand how adiesel can“runaway”.

(ON SLIDE #131)

(b)

Measuring Volumetric Efficiency.

Volumetricefficiency is expressed as a ratio of the amount of air that entersthe cylinders on the intake stroke to the amount of mixture that thecylinders could actually hold.

(ON SLIDE #132)

The following factors will decrease volumetric efficiency:

(1)The shorter the duration of the intake stroke(higher RPM) the lower the efficiency.

(2) As the air passes through the engine on itsway to the cylinder, it picks up heat. As the air heats up, itbecomes less dense. This means that less air actually enters thecylinder.

(4) Elevation also affects volumetric efficiency.An increase in elevation will decrease the density of air.

(ON SLIDE #133)

(5)

Increasing Volumetric Efficiency.

Any increase involumetric efficiency will increase engine performance. Volumetricefficiency may be increased by doing the following.

(a)Keep the intake air cool. By ducting intake airfrom outside of the engine compartment, the intake air can be keptcooler. The cooler the air is, the higher the volumetric efficiencywill be. This is because a cool air is denser or more tightly packed.

(b) Modify the intake passages. Any changes to theintake passages that make it easier for the air to flow through willcause an increase in volumetric efficiency. Other changes includereshaping ports to smooth out bends, reshaping the back of the valveheads, or polishing the inside of the ports.

(c) Altering the time that the valves open or how farthey open, volumetric efficiency can be improved.

(d)Turbocharging, the volumetric efficiency figurecan be brought to over 100 percent.

(ON SLIDE #134)

b.

Valves.

TheI-head configuration is the most popular for currentdiesel engines and gets its name from the letter formed by the pistonand the valve. These engines have their camshafts located in theircylinder blocks. These engines are also known as the

Each cylinder in a four-stroke cycle enginemust have one intake and one exhaust valve to allow fresh (oxygenrich) air into each cylinder, and allow burnt (inert) gasses toescape. The valves are commonly of the poppet design. The word poppetis derivedfrom the popping action of the valve. The valve shape thatis used in a given engine design is dependent upon the requirementsand combustion chamber shape.

(ON SLIDE #136)

(2)Construction.

Construction and design considerationsare very different between intake and exhaust valves. The differenceis based on their temperature operating angles. Intake valves arekept cool by the incoming intake air. Exhaust valves are subject tointense heat from the burnt gases that pass by it. The temperature ofthe exhaust valve can be in excess of 1,300 ºF (704.4 ºC). Intakevalves are made of a nickel chromium alloy. Exhaust valves are madeof a silichrome alloy. Some exhaust valves use a special hard facingprocess that keeps the face of the valve from taking on theshape ofthe valve seat at high temperatures.Stems may be hollow and filledwith sodium to improve heat transport and transfer.

(ON SLIDE #137)

Older air cooled engines used exhaust valves were hollowed out andpartially filled with metallic sodium. The sodium, which liquefied atoperating temperatures, splashed between the valve head, where itpicked up heat, and the valve stem, where the heat is

transferred tothe valve guide.

(ON SLIDE #138)

(3)

Valve Seats.

The valve seats are very important, asthey must match the face of the valve head to form a perfect seal.The seats are made so that they are concentric with the valve guides;that is, the surface of the seat is an equal distance from the centerof the guide all around.

(ON SLIDE #139)

There are three common angles that are used when machining the valveseat; they are 15, 30, and 45 degrees (dependent on manufacturerspecs.). The face of the valve is usually ground with a ½º to a 1ºdifference to help the parts seat quickly.

(ON SLIDE #140)

By reducing the contact area, the pressure between the mating partsis increased, thereby forming a better seal. The valve seats can beeither part of the cylinder head or separate inserts. Valve seatinserts generally are held into the head by an interference (squeeze)fit. The head is heated in an oven to a uniform high temperature andthe seat insert is shrunk by cooling it in dry ice. While the twoparts are at opposite temperature extremes, the seat insert ispressed into place.

(ON SLIDE #141)

(4)

Valve Guides.

The valve guides are the parts thatsupport the valves in the head

and are machined to a fit with

a fewthousandths ofan inch clearance from

the valve stem. Valve guidesmay be cast integrally with the head, or they may be removable.Removable valve guides are usually press fitted into the head. Thisclose clearance is important for the following reasons:

(a)It keeps the lubricating oil from

getting into thecombustion chamber.

(b)It keeps exhaust gases from getting into thecrankcase area past the exhaust valve stems during the exhauststroke.

(c)It keeps the valve face in perfect alignment withthe valve seat.

(ON SLIDE #142)

(5)Valve Springs, Retainers, and Seals.

The valve assemblyis completed by the spring, retainer, and seal. Before the spring andthe retainer fit into place, a seal is placed over the valve stem.The seal acts like an umbrella to keep the valve operating mechanismoil from running down the valve stem and into the combustion chamber.

(ON SLIDE #143)

The spring, which keeps the valve in a normally closed position, isheld in place by the retainer. The retainer locks onto the valve stemwith two wedged-shaped parts that are called valve keepers.

(ON SLIDE #144)

(ON SLIDE #145)

(6)

Valve Rotators.

(a)Purpose.

It is common in heavy-duty applicationsto use mechanisms that make the exhaust valves rotate. They keepcarbon from building up between the valve face and seat, which couldhold the valve partially open, causing it to burn.

(ON SLIDE #146)

(b)

Types.

(1) The release-type rotator releases the springtension from the valve while open. The valve then will rotate fromengine vibration.

INSTRUCTOR NOTE

Computer aided graphic valve keeper 0.10 minutes.

(2) The positive rotator is a two-piece valveretainer with a flexible washer between the two pieces. A series ofballs between the retainer pieces roll on machined ramps as pressureis applied and released from the opening and the closing of thevalve. The movement of the balls up and down the ramps translatesinto rotation of the valve.

(ON SLIDE #147)

(7)

Valve Train.

It is obvious that it is very important tooperate the valves in a timed sequence. If the exhaust valve openedin the middle of the intake stroke, the piston would draw burnt gasesinto the combustion chamber with a fresh air. As the piston continuedtothe power stroke, there would be nothing in the combustion chamberthat would burn. The valves in overhead valve engines use additionalcomponents to link the camshaft to the valves. Overhead valve enginesuse push rods and rocker arms.

(ON SLIDE #148)

(a)

Push Rods.

Push rods usually are constructed ofhollow steel. Most air-cooled engines use the push rods to supplylubricant to the upper valve mechanism.

(ON SLIDE #149)

(b)

Rocker Arms.

Rocker arms are manufactured ofsteel, aluminum, or cast iron. The most common for current use arecast iron rockers. They are used in larger, low-speed engines. Theyalmost always pivot on a common shaft.

The provision for adjustingvalve clearance on solid tappet, valve-in-head engines is usually inthe form of a screw on the rocker arm. On overhead valve (or push rodengines), there is usually a screw-type adjustment where the push rodactuates it. The adjusting screw can either be of the self-lockingtype, or have a jam nut to lock it.

(ON SLIDE #151)

(d)

The crankshaft must make two complete revolutionsto complete one operating cycle. Using these two facts, a camshaftspeed must be exactly one-half the speed of the crankshaft. Toaccomplish this, the timing gears are made so that the crankshaftgear hasexactly one-half as many teeth as the camshaft gear. Thetiming marks are used to put the camshaft and the crankshaft in theproper position to each other.

(ON SLIDE #152)

(8)

Valve Timing.

(a)

General.

Valve timing is a system developed formeasuring in relation to the crankshaft position (in degrees), thepoints when the valves open, how long they stay open, and when theyclose. Valve timing is probably the single most important factor intailoring anengine for specific needs. By altering valve timing, anengine can be made to produce its maximum power in a variety of,speed ranges. The following factors together make up a valveoperating sequence.

INSTRUCTOR NOTE

Computer aided graphic valve adjustment 2.35 minutes.

INSTRUCTOR NOTE

Computer aided graphic gear train timing 0.08minutes.

1

Opening and Closing Point. The opening andclosing

points are the positions of the crankshaft (in degrees) whenthe valve just begins opening and just finishes closing.

2

Duration. Duration is the amount of crankshaftrotation (in degrees) that a given valve will remain open.

It can bemodified to change power output. (EX Larger Cam)

3

Valve Overlap. Valve overlap is a period in thefour-stroke cycle when the intake valve opens before the exhaustvalve closes.

(ON SLIDE #153)

(9)

Valve Timing Considerations.

Throughout the crankshaftrevolution, the speed of the piston changes. From a stop at thebottom of the stroke, the piston will reach its maximum speed halfwaythrough the stroke and gradually slow to a stop as it reaches the endof the stroke. The piston

will behave exactly the same on the down

stroke. There are two periods of crankshaft rotation in which thereis almost no perceptible movement of the piston. One of these periodsbegins at approximately 15º to 20º before top dead center and ends atapproximately 15º to 20º after top dead center. The other periodbegins at approximately 15º to 20º before bottom dead center and endsat approximately 15º to 20º after bottom dead center. These twoperiods of crankshaft rotation are utilized when establishing a

valvetiming sequence as follows.

(a) During the period that occurs at top dead center,valve overlap is introduced to increase volumetric efficiency. Byopening the intake valve before the exhaust valve is closed, theintake is pulled in by the momentum

of the exiting exhaust gas. Theintake coming in also helps to sweep or scavenge the cylinder ofexhaust gases. Because the overlap occurs during one of the periodsof little piston movement, there is no problem with exhaust beingpushed into the intake port or exhaust gas being pulled into thecylinder through the exhaust port by the piston.

(b) During the period that occurs at bottom deadcenter, the pressure

remaining in the cylinder at the end of thepower stroke is utilized by opening the exhaust valve early. When theexhaust valve opens, the pressure in the cylinder starts pushing theexhaust gas out of the cylinder. Because the final 15º to 20º of thepower stroke have almost no piston movement, there is no problem withexhaust being drawn in by the

piston. As stated earlier, engines canbe designed to produce power in a specific speed range by alteringvalve timing. By increasing the valve duration and overlap, an enginecan be made to produce more power in the higher speed ranges. This isbecause the exiting exhaust gas will have more inertia, making itsscavenging effect last longer. This same engine will run poorly atlow speed due to the piston having a tendency to pull exhaust backinto the cylinder and blow it back up into the intake port.

(ON SLIDE #154)

(ON SLIDE #155)

c.Turbocharging/Supercharging.

(ON SLIDE #156)

(1)

Turbocharging is a method of increasing enginevolumetric efficiency by forcing the air into the intake rather thanmerelyallowing the pistons to draw it in naturally. Turbocharging insome cases will push volumetric efficiencies over 100 percent.Engines must be modified to operate properly in some cases, becausethe extra air will cause higher compression pressures.

(ONSLIDE #157)

(2)

A turbocharger uses the force of the engine exhauststream to force the air into the engine. It consists of a housingcontaining two chambers. One chamber contains a turbine that is spunas hot exhaust gases are directed against it. The turbine shaftdrives an impeller that is located in the other chamber. The spinningimpeller draws an air and forces it into the engine. Because thevolume of exhaust gases increases with engine load and speed, theturbocharger speed will increase proportionally, keeping the

manifoldpressure boost fairly uniform.

INSTRUCTOR NOTE

The Marine Corps current stock of constructionequipment has only two examples of naturallyaspirated diesel engines the 7½ Ton Crane (Cummins B3.9 L) and the ACE (Cummins 903).

INSTRUCTOR NOTE

Computer aided graphic air intake1 0.18 minutes.

INSTRUCTOR NOTE

Computer aided graphic turbochargers 0.20 minutes.

(ON SLIDE #158)

(3)

A device known as a waste gate is installed onturbocharged engines to control manifold pressure. It is a valvethat, when open, allows engine exhaust to bypass the turbochargerturbine, effectively reducing intake pressure. The waste

gate valveis operated by a diaphragm that is operated by manifold pressure. Thediaphragm will open the waste-gate valve whenever manifold pressurereaches the desired maximum.

(ON SLIDE #159)

(4)

Many late model engines which are turbocharged employan after

cooler to further improve the engine efficiency. Aftercoolers (also called inter

coolers or heat exchangers) are smallradiators positioned between the compressor housing of theturbocharger and the inlet manifold of the engine.

(a) Water cooled intercoolers are the design common toindustrial diesel engines. Coolant enters the intercooler and passesthrough the core tubes and back into the cylinder block or cylinderhead. Air from the turbocharger (compressor) flows around the tubesand is cooled before it enters the inlet manifold. This increases thepower output by about 10% to 20% because the incoming air is cooledto within 40° F of the engine coolant temperature and, therefore,more air enters the cylinders.

(b) The result is

lower cylinder pressure, moreeffective cooling of the cylinder components, and a lower exhaust gastemperature. Without the intercooler, the air temperature enteringthe intake manifold would increase sharply because of the compressionof the air and because of heat from the turbocharger. This wouldresult in a loss in air density and power, and elevated cylinder andexhaust gas temperatures.(approximately 1° increase in air intaketemperature will increase the exhaust temperature increases by 3° F).

INSTRUCTOR NOTE

Computer aided graphic wastegates 0.15 minutes.

INSTRUCTOR NOTE

Computer aided graphic after

coolers 0.27 minutes.

(ON SLIDE #160)

(5)

Superchargers increase intake by compressing air aboveatmospheric pressure, without creating a vacuum. This forces more airinto the engine, providing a “boost.” With the additional air in theboost, more fuel can be added to the charge, and the power of theengine is increased. Supercharging adds an average of 46 percent morehorsepower. And 31 percent more torque. In high-altitude situations,where engine performance deteriorates because the air has low densityand pressure, a supercharger delivers higher-pressure air to theengine so it can operate optimally.

(ON SLIDE #161)

(a)Differences. Unlike turbochargers, which use theexhaust gases created by combustion to power the compressor,superchargers draw their power directly fromthe crankshaft. Thisgives them direct power and no turbo lag. Most are driven by anaccessory belt, which wraps around a pulley that is connected to adrive gear. The rotor of the compressor can come in various designs,but its job is to draw air in, squeeze the air into a smaller spaceand discharge it into the intake manifold.

(b)To pressurize the air, a supercharger must spinrapidly,more rapidly than the engine itself. Making the drive gearlarger than the compressor gear causes the compressor to spin faster.Superchargers can spin at speeds as high as 50,000 to 65,000rotations per minute (RPM).A compressor spinning at 50,000 RPMtranslates to a boost of about six to nine pounds per square inch(psi). That's six to nine additional psi over the atmosphericpressure at a particular elevation. Atmospheric pressure at sea levelis 14.7 psi, so a typical boost from a supercharger places about 50percent more air into the engine. Superchargers may also useintercoolers.

(ON SLIDE #162)

(6)

Exhaust emissions.

When the fuel is burned in thecombustion chamber, the ideal situation would be to have the fuelcombine completely with the oxygen from the intake air. The carbonwould then combine to form carbon dioxide (CO2), the hydrogen would

combine to form water (H20), and the nitrogen that is present in theINSTRUCTOR NOTE

intake air would stand alone. The only other product present in theexhaust would be any oxygen from the intake air that was not used inthe burning of the fuel.

(ON SLIDE #163)

In areal life situation however, this is not what happens. The fuelnever combines completely with the oxygen and undesirable exhaustemissions are created as a result. Normally a diesel engine has moreair available than what is used and the fuel delivery system isprecisely timed to be injected when combustion chamber pressure andtemperature is optimal for complete burning of the fuel. Majorpollutants include:

(a)Carbon Monoxide (CO).

Carbon monoxide is formed asa result of combustion chamber pressures (temperatures) that are toolow. A cold engine will produce more Carbon Monoxide until it reachesoperating temperature when emissions will become

extremely low.Carbon monoxide is a colorless, odorless gas that is poisonous.

(b)Nitrogen oxides

(NOx).

Oxides of nitrogen areformed when the nitrogen and oxygen in the intake air combine due tothe high temperatures of combustion. Oxides of nitrogen are harmfulto all living things.

(c)Sulfur dioxide (SO2)

is generated from the sulfurpresent in diesel fuel. The concentration of SO2

in the exhaust gasdepends on the sulfur content of the fuel. Sulfur dioxide is acolorless toxic gas with a characteristic, irritating odor. Oxidationof sulfur dioxide produces sulfur trioxide which is the precursor ofsulfuric acid. Sulfur oxides have a profound impact on environmentbeing the major cause of acid rain.

(ON SLIDE #164)

(d)Hydrocarbons (HC).

Hydrocarbons are unburned fuel.They are particulate in form (solid) and, like carbon monoxide, theyare manufactured by combustion chamber pressures (temperatures) thatare too low. Hydrocarbons are harmful to all living things. In anyurban area where vehicular traffic is heavy, hydrocarbons in heavyconcentrations react with sunlight to produce a brown fog known asphotochemical smog.

(ON SLIDE #165)

1

Diesel particulate matter (DPM), is defined bythe EPA regulations as a complex aggregate of solid and liquidmaterial.Diesel particulates are very fine. The carbonparticles mayhave a diameter of 0.01-

1 micron range. As such, diesel particulatematter is almost totally inhalable and has a significant healthimpact on humans. It has been classified by several governmentagencies as either "human carcinogen" or "probable human carcinogen".It is also known to increase the risk of heart and respiratorydiseases.

(ON SLIDE #166)

2

Polynuclear Aromatic Hydrocarbons (PAH) arehydrocarbons containing two or more benzene rings. Many compounds inthis class are known human carcinogens. PAH’s in the exhaust gas aresplit between gas and particulate phase. The most harmful compoundsof four and five rings are present in the organic fraction of DPM(SOF).

(ON SLIDE #167)

(7)

Controlling of Exhaust Emissions.

The control ofexhaust emissions is a very difficult job. To eliminate carbonmonoxide and hydrocarbon emissions, the temperatures of thecombustion chamber would have to be raised to a point that would meltpistons and valves. This is compounded with the

fact that oxides ofnitrogen emissions go up with any increases in combustion chambertemperatures. Knowing these facts, it can be seen that auxiliaryemission control devices are necessary.

(a)Draft Tube System.

Older engines used a verysimple systemthat vented blowby to the atmosphere through a drafttube. The draft tube extends from an area of the crankcase that isabove oil level to a point of exit that project straight downwardunder the equipment. The outlet of the tube is cut on a slant upwardtoward the rear of the equipment. With this shape outlet, suction iscreated by the forward movement of the equipment. Circulation offresh air will occur in the crankcase with the addition of a breathercap also located at a point on the crankcase above oil level.

(b) The negative pressure created at the end of thedraft tube will cause air to be drawn In through the crankcasebreather. A wire mesh filter is built into the breather to keep dirtout of the crankcase.

(c) The draft tube contains a sedimentchamber and awire mesh filter at the point where it attaches to the crankcase. Itspurpose is to trap any oil that tries to leave through the draft tubeand return it to the crankcase.

(d) By strategic location of the breather cap anddraft tube and theuse of baffles, a complete purging of crankcaseblowby fumes is ensured. The draft tube system is obsolete nowbecause it discharged excessive hydrocarbon emissions directly intothe atmosphere. It also did not keep the crankcase as clean as thepositive crankcase ventilation system. This is because it relied onthe movement of the vehicle to activate it. As a result of this,draft tube-equipped engines were very prone to sludge buildup.

(8)

Positive Crankcase Ventilation (PCV) System.

Thepositive crankcase ventilation system utilizes turbocharger vacuum topurge the crankcase of blowby fumes. The fumes are then aspiratedback into the engine where they are reburned.

(a) A hose is tapped into the crankcase at a point thatis well above the engine oil level. The other end of the hose is tappedinto the piping before the turbocharger.

(b) An inlet breather is installed on the crankcase ina location that is well above the level of the engine oil. The inletbreather also is located strategically to ensure complete purging ofthe crankcase by fresh air.

(c) The areas of the crankcase where the hose and theinlet breather are tapped have baffles to keep the motor oil fromleaving the crankcase.

(d) A flow control valve (called a PCV valve) isinstalled in the line that connects the crankcase to vacuum. It isand serves to avoid the air mixture by doing the following:

(ON SLIDE #168)

(9)

Exhaust Smoke Diagnosis.

Good mechanics go into actionquickly, making simple observations and tests that set limits to theproblem. A strong familiarization with how the components worktogether will help the mechanic to limit tests to the most likelycause.

(ON SLIDE #169)

NEVER ASS-U-ME

corrective action based on this initial indication,only which tests should be performed first before making a diagnosis.

(a)

Distinguishing between conditions that affect allcylinders and those that affect one or two is a simple first step.

1

General

malfunctions discolor the whole exhauststream such as too much advance on pump timing will send allcylinders into detonation.

2

Single cylinder malfunctions can generate puffsof smoke such as the clatter caused by a faulty injector will belimited tothe associated cylinder.

(b)After determining whetherit’s

one or allcylinders, the next step is to determine why. White smoke means oneor more fueled, but misfiring cylinders, and usually accompanies coldstarts (in a warm engine it may indicate low

Light blue or whitishsmoke at high speedunder light load.Pungent odor.

Over-cooling.

Replacethermostat.

(ON SLIDE #172)

(ON SLIDE #173)

INSTRUCTOR NOTE

Finish the class by watching Cummins

“Turbochargingand Intake Air Cooling”. (Approximately 30 minutes.)

INSTRUCTOR NOTE

Picture of Semi truck exhaust

(ON SLIDE #174)

TRANSITION: So far we have discussed diesel engine intake and exhaustsystems. Are there any other questions? If not let’s move on to thepractical application of removing the intake and exhaust systems.

HRS)In groups no larger than 5 the studentswill have their assigned toolboxes, technical manuals and assignedengines with work stations. There will be at least one instructorsupervising the exercise. The purpose of this practical applicationis to remove the intake and exhaust systems.

PRACTICE:

In their groups the students will follow the technicalmanuals to disassemble and remove the intake and exhaust systems ontheir assigned engines.

PROVIDE HELP:The instructormayassist in the disassembly process

ifneeded.

1. Safety Brief:At all times proper PPE will be worn to includesafety boots. Safety glasses will be worn anytime fuel or liquidunder pressure is being used.

2.Supervision and Guidance:The instructor will walk around to thedifferent groups and supervise the disassemblyanswering anyquestions the students may have.

(ON SLIDE #175)

TRANSITION:

Over the past 1.15 hours we have reviewed enginerespiration and how the components worktogether, are there anyquestions? I have some questions for you.

The lubrication system in an engine supplies aconstant supply of oil to all moving parts. This constant supply offresh oil is important to minimize wear, flush bearing surfacesclean, and remove the localized heat that develops between movingparts as a

result of friction. In addition, the oil that is suppliedINSTRUCTOR NOTE

Computer aided graphic Oil in your engine 25 minutes.

INSTRUCTOR NOTE

Computer aided graphic wearanalysis 1.15 minutes.

INSTRUCTOR NOTE

Computer aided graphic wear analysis 1.15 minutes.

Computer aided graphic lubrication purpose 0.10

minutes.

Computer aided graphic friction 0.21 minutes.

QUIZ

(30min)

Hand out quiz for

diesel engine intake and exhaust

system operation and troubleshooting quiz. Give thestudents 20 minutes to complete and review it withthe students after.

to the cylinder walls helps the piston rings make a good seal toreduce blowby.

(ON SLIDE #179)

b.Engine Oil Characteristics.

The primary function of engineoil is to reduce friction betweenmoving parts (lubricate). Friction,in addition to wasting engine power, creates destructive heat andrapid wear of parts. The greater the friction present between movingparts, the greater the energy required to overcome that friction. Theincrease in energy adds to the amount of heat generated, causingmoving parts that are deprived of oil to melt, fuse, and seize aftera very short period of engine operation. The effectiveness of amodern lubrication system makes possible the use of friction-typebearings in an engine. Friction between the pistons and the cylinderwalls is severe, making effective lubrication of this areaimperative. Lubrication of the connecting rod and main bearings iscrucial because of the heavy loads that are placed on them. There aremany other less critical engine parts that also need a constantsupply of oil, such as the camshaft, valve stems, rocker arms, andtiming gears.

(1)

Oil as a Lubricant.

(a) Every moving part of the engine is designed tohave a specific clearance between it and the bearing it moves on. Asoil is fed to the bearing it forms a film, preventing the rotatingpart from actually touching the bearing.

(b) As the part moves, the film of oil acts as aseries of rollers. Because the moving parts do not actuallytoucheach other, friction is reduced greatly.

(ON SLIDE #180)

INSTRUCTOR NOTE

Computer aided graphic wear analysis 1.15 minutes.

Computer aided graphic lubrication purpose 0.10

minutes.

Computer aided graphic friction 0.21 minutes.

Computeraided graphic using plasti-gauge 1.49 minutes.

INSTRUCTOR NOTE

If the engines are taken apart and if time permits,each group can check the bearing clearances on onecrank shaft journal.

(c) It is important thatsufficient clearance beallowedbetween the part and the bearing. Otherwise the film might betoo thin. This would allow contact between the parts, causing thebearing to wear or burn up.

(d) It also is important that the clearance not be toolargebetween rotating parts and their bearings. This is trueparticularly with heavily loaded bearings like those found on theconnecting rods. The heavy loads could then cause the oil film to besqueezed out, resulting in bearing failure.

(ON SLIDE #181)

(2)

Oil as a Coolant.

Engine oil circulated throughout theengine also serves to remove heat from the friction points. The oilcirculates through the engine and drains to the sump. The heat pickedup by the oil while it is circulated is removed by airflow around theoutside of the sump. In some instances where the sump is not exposedto a flow of air, it is necessary to add an oil cooling unit thattransfers the heat from the oil to the engine cooling system.

(ON SLIDE #182)

(3)

Oil Contamination.

Oil does not wear out but it doesbecome contaminated. When foreign matter enters through the airintake, some of it will pass by the piston rings and enter thecrankcase. This dirt, combined with foreign matter entering throughthe crankcase breather pipe, mixes with the oil, and when forced intothe bearings, greatly accelerates wear. Water, one of the products ofcombustion, will seep by the piston rings as steam and condense inthe crankcase. The water in the crankcase then will emulsify with theoil to form a thick sludge. Products of fuel combustion will mix withthe oil as they enter the crankcase through blowby. The oil, whenmixed with the contaminants, loses its lubricating qualities andbecomes acidic. Engine oil must be changed periodically to preventcontaminated oil from allowing excessive wear and causing etching ofbearings.

(ON SLIDE #183)

Oil contamination is controlled in the following ways.

(a)Controlling engine temperature.

A hotter runningengine burns its fuel more completely and

evaporates the waterproduced within it before any appreciable oil contamination occurs.

(b) The use of oil filters removes particles from theoil before it reaches the bearings, minimizing wear.

(c) An adequate crankcase ventilation system willpurge

the crankcase of blowby fumes effectively before a large amountof contaminants can mix with the oil.

(d) The use of air intake filters trap foreignmaterial and keeps it from entering the engine.

(ON SLIDE #184)

(4)

Oil Dilution.

Engine oil thins outwhen mixed withfuel, causing a dramatic drop in its lubricating qualities. Some ofthe causes of oil dilution are the following.

There are some fuelinjection pumps (such as the distributor type) that have the oil andfuel in close proximity. When these types of pumps fail the crankcasecan and will fill with fuel.

(c) An engine with

a malfunctioning thermostat or anengine that is operated for only short durations will never reach asufficient temperature to burn the fuel completely. A small amount ofoil dilution occurs in all engines from initial startup through warmup. When the engine reaches its operational range 180°F (82.2°C) to200°F (93.3°C)), however, this condition is corrected as the excessfuel vaporizes in the crankcase and is carried off by the crankcaseventilation system.

(ON SLIDE #185)

(5)

American Petroleum Institute (API) Rating System.

TheAPI system for rating oil classifies oil according to its performancecharacteristics. The higher rated oils contain additives that providemaximum protection against rust, corrosion, wear, oil oxidation, andthickening at high temperatures. The higher the alpha designation,the higher quality the oil is.

(ON SLIDE #186)

(6)

Oil Viscosity.

The viscosity of oil refers to itsresistance to flow. When oil is hot, it will flow more rapidly thanINSTRUCTOR NOTE

Computer aided graphic acid and contaminants in the

Oil .17 minutes

when it is cold. In cold weather, therefore, oil should be thin (lowviscosity) to permit it to retain its film strength. The ambienttemperature in which a vehicle operates determines weather an engineoil of high or low viscosity should be used. If, for example, toothin an oil were used in hot weather, consumption would be highbecause It would leak past the piston rings easily. The lubricatingfilm would not be heavy enough to take up bearing clearances orprevent bearing scuffing. In cold weather, heavy oil would not giveadequate lubrication because its flow would be sluggish; some partsmight not receive oil at all.

(ON SLIDE #187)

(a)

Oils are graded according to their viscosity by aseries Society of Automotive Engineers (SAE) numbers. The viscosityof the oil will increase progressively with the SEA number. An SAE 4oil would be very light (low viscosity) and SAE 90 oil would be veryheavy (viscosity). It should be noted that the SAE number of the oilhas nothing to do with the quality of the oil. The viscosity numberof the oil is determined by heating the oil to a predeterminedtemperature and allowing it to flow through a precisely sized orificewhile measuring the rate of flow. The faster oil flows, the lower theviscosity. Any oil that meets SAE low temperature requirements willbe followed by the letter W (winter). An example would be SAE 10W.

(b)Multiweight Oils.

Multiweight oils aremanufactured to be used in most climates because they meet therequirements of a light oil in cold temperatures and of a heavy oilin hot temperatures. Their viscosity rating will contain two numbers.An example of this would be 10W-30. An oil with a viscosity

rating of10W-30 would be as thin as a 10W weight oil at 0ºF (-17.7ºC) and 30weight at 210 degrees F

(c)

Detergent Oils.

Detergent oils contain additivesthat help keep the engine clean by preventing the formation of sludgeand gum.

(ON SLIDE #188)

INTERIM TRANSITION: Now that we have covered what oil is and what itdoes are there any other questions? Let’s go ahead and take a 10minute break.

Oil pumps are mounted eitherinside or outside of the crankcase, depending on the design of theengine. They are usually mounted so that they can be driven by geardirectly from the camshaft. The rotor oilpump makes use of an innerrotor with lobes that match similarly shaped depressions in the outerrotor. The inner rotor is off center from the outer rotor. The innerrotor is driven and, as it rotates, it carries the outer rotor aroundwith it. The outer rotor floats freely in the pump bodyby.

(ON SLIDE #190)

(2)

Crescent-Type Oil Pump.

The crescent pump isadvantageous in situations where high delivery rate of oil isrequired, particularly at low engine speeds. The basic principle isthe same; two rotating wheels build oil pressure near the deliverynozzle. Movements of the two wheels are in tandem as opposed tocontrary wheel movements in the gear and rotary pumps. Due to sizedifference of the two wheels, oil is carried to the delivery nozzleand pressure created by gradually reducing the size of thecontainment area or the crescent formed between the two wheels.

(ON SLIDE #191)

(3)

Gear-Type Oil Pump.

Gear pumps operate on the waterwheel principle. They have two wheels to create high pressure in theoil pan and inject the oil into all areas that need lubrication. Asthe engine willbe operating at high speeds, high pressure isrequired for the oil to reach all moving parts in the engine. Twointerlocking wheels inside the pump draw oil from the pan and forceit into relatively smaller area and build the required pressure. Themovements of the wheels or gears and the sides of the pump are sodesigned that when high pressure is formed near the delivery nozzle,oil will not flow back into the oil pan.

(ON SLIDE #192)

d.

Oil Strainer and Pickup.

Most manufactures of in-line and V-type engines place at least one oil strainer or screen in thelubrication system. The screen is a fine mesh bronze screen that islocated in the oil pump on the end of the oil pickup tube. The oilpickup tube then is threaded directly into the pump inlet or mayattach to the pump by a bolted flange. A fixed-type strainer, likethe one described, is located so that a constant supply of oil willbe assured. The oil strainer is used to filter out larger particlesor contaminates.

(ON SLIDE #193)

e.

Oil Filters.

(1)

Purpose.

The oil filter removes most of the impuritiesthat have been picked up by the oil as it is circulated through theengine. The filter is mounted outside of the engine and is designedto be replaceable readily.

(ON SLIDE #194)

(2)Filter Configurations.

There are two basic filterelement configurations: the cartridge type and the sealed canistertype.

(a) The cartridge-type filter element fits into apermanent metal container. Oil is pumped under pressure into thecontainer, where it passes from the outside of the filter element tothe center. From here the oil exits the container. The element ischanged easily by removing the cover from the container when thistype of filter is used.

(b) The sealed canister-type filter element iscompletelyself-contained, consisting of an integral metal containerand filter element. Oil is pumped into the container on the outsideof the filter element. The oil then passes through the filter mediumto the center of the element, where it exits the container. This typeof filter is screwed onto its base and is removed by spinning it off.

(3)

Filter Medium Materials.

(a) Cotton waste or resin-treated paper are the twomost popular filter mediums. They are held in place by sandwichingthem between two perforated

metal sheets.

INSTRUCTOR NOTE

Computer aided graphic abrasive and erosive wear 2.31minutes.

(b) Some heavy-duty applications use layers of metalthat are thinly spaced apart. Foreign matter is strained out as theoil passes between the metal layers.

(ON SLIDE #195)

(4)

Filter System Configuration.

The full-flow system isthe most popular in current engine design. All oil in a full-flowsystem is circulated through the filter before it reaches the engine.When a full-flow system is used, it is necessary to incorporate abypass valve in the oil filter to allow the oil to circulate throughthe system without passing through the element in the event that itbecomes clogged. This will prevent the oil supply from being cut offto the engine.

(ON SLIDE #196)

f.

Pressure Regulator.

The oil pump will produce pressures ingreat excess. This excess pressure, if uncontrolled, would causeexcess oil consumption due to flooded cylinder walls and leakagethrough oil seals. A spring-loaded regulator valve is installed inthe lubrication system to control pump pressure. The valve will openas the pressure reaches the value that is determined by the spring,causing excess oil to be diverted back to the crankcase.

(ON SLIDE #197)

g.Crankshaft Bearings (Friction Type).

The crankshaft issupported in the crankcase and rotates in the main bearings. Theconnecting rods are supported on the crankshaft by the rod bearings.

One of the main bearings serves as the thrust bearing which preventsexcessive axial movement.

There are also anti friction type bearingssuch as ball bearings but they are not used as crankshaft bearings.

INSTRUCTOR NOTE

Computer aided graphic full flow system 0.08 minutes.

INSTRUCTOR NOTE

Computer aided graphic by-pass valves 1.33 minutes.

(ON SLIDE #198)

(1)

Construction.

Crankshaft bearings are made as precisioninserts. They simply slip into place in the upper and lower halves ofthe shells. When the halves are clamped together, they form aprecision bearing that will be a perfect fit for a properly sizedshaft. The bearing inserts and the mating surface that hold them mustbe sized perfectly. The insert merely slips into place and is heldfrom turning by the locating tab. The crankshaft sits on the lowerbearing shelf.

(ON SLIDE #199)

(2)

Materials.

Most bearings begin

with a steel backing togive them rigidity. The lining then is applied to the steel backing.The lining usually consists of an alloy of copper, tin, and lead. Thelining also may be made of babbit. Babbit is a popular bearingmaterial that is an alloy consisting of copper, tin, and antimony.The lining thickness usually ranges from 0.002 to0.005 in. (0.051 to0.127 mm). The bearing then is coated with either aluminum or tin toa thickness of approximately 0.001 in. (0.025 mm).

(ON SLIDE #200)

(3)

Bearing

Requirements.

Bearings must be able to supportthe crankshaft rotation and deliver power stroke thrusts under themost adverse conditions. A good bearing must have the followingqualities.

(ON SLIDE #201)

(a)Strength.

Engine bearings are constantly subjectedto tremendous forces from the thrust of the power strokes. Thebearings must be able to withstand these loads without spreading outor cracking.

INSTRUCTOR NOTE

Computer aided graphic main bearing shells 0.17minutes.

INSTRUCTOR NOTE

Computer aided graphicstress wear 2.40 minutes.

(ON SLIDE #202)

(b)Corrosion resistance.The bearing must beresistant to moisture and acids that always are present in thecrankcase.

(ON SLIDE #203)

(c)Antiscuffing.

The bearing surface should be ableto absorb enough oil to keep It from scuffing during startup, or anyother time when It must run momentarily without an oil supply.

(ON SLIDE

#204)

(d)Embedabillty.

The surface of the bearing must besoft enough to allow particles of foreign matter to embed themselvesand prevent damage of the shaft journal.

(ONSLIDE #205)

(e)Conformability.

The bearing must be able toconform or fit itself to the surface of the crankshaft Journal.

(ON SLIDE #206)

(f)Conductivity.

The bearings must be able to conductheat to the connecting rod so that they will not overheat.

INSTRUCTOR NOTE

Computer aided graphic lubrication corrosion 1.59minutes.

INSTRUCTOR NOTE

Computer aided graphic adhesive wear 1.52 minutes.

INSTRUCTOR NOTE

Computer aided graphic embedability 0.49 minutes.

INSTRUCTOR NOTE

Computer aided graphic conductivity 0.24 minutes.

(g)Resistance to Heat.

The bearing must be able tomaintain all of these characteristics throughout its entire operatingtemperature range.

(ON SLIDE #207)

(4)

Connecting Rod Lubrication.

The connecting rod bearingsfit into the lower end of the connecting rod. They are fed a constantsupply of oil through a hole in the Crankshaft Journal. A hole in theupper bearing half feeds a passage in the connecting rod to provideoil to the piston pin.

(ON SLIDE #208)

(5)Crankshaft Main Bearings.

The upper halves of the mainbearings fit right into the crankcase, and the lower halves fit intothe caps that hold the crankshaft in place.

The main bearings have holes drilled in their upper halves throughwhich a supply of oil is fed to them. The crankshaft has holesdrilled in the journals that receive oil from the main bearings tofeed the rod bearings. It is a common practice to cut a groove In thecenter of the main bearing Inserts. This suppliesa more constantsupply of oil to the connecting rod bearings.

(ON SLIDE #209)

One of the main bearings also serves as a thrust bearing. Thiscontrols back and forthmovement of the crankshaft. This thrustbearing is characterized by side flanges.

(ON SLIDE #210)

h.

Lubrication System.

A complete pressurization of lubricationis achieved in the force-feed lubrication system. Oil is forced bythe oil pump from the crankcase to the main bearings and the camshaftbearings. The connecting rod bearings are also fed oil under pressurefrom the pump. Oil passages are drilled in the crankshaft in order tolead oil to the connecting rod bearings. The passages deliver oilfrom the main bearing journals to the rod bearing journals. In someengines, these openings are holes that index (line up) once

crankshaft revolution. In other engines, there are annular grooves inthe main bearings through which oil can feed constantly into the holein the crankshaft. The pressurized oil that lubricates the connectingrod bearings goes on to lubricate the pistons and walls by squirtingout through strategically drilled holes. This lubrication system isused in virtually all engines that are equipped with semi or fullfloating piston pins.

(ON SLIDE #211)

TRANSITION:Over the past 1.15 hours we have reviewed enginelubrication, how frictional losses are minimized, and how engine lifeis maximized.

HRS)In groups no larger than 5 the studentswill have their assigned toolboxes, technical manuals and assignedengines with work stations. There will be at least one instructorsupervising the exercise. The purpose of this practical applicationis to remove and drain the engine oil pan and pump.

PRACTICE:

In their groups the students will follow the technicalmanuals to drain and remove the engine oil pan and pump on theirassigned engines.

PROVIDE HELP:The instructor may assist in the disassembly processifneeded.

1. Safety Brief:At all times proper PPE will be worn to includesafety boots. Safety glasses will be worn anytime fuel or liquidunder pressure is being used.

2.Supervision and Guidance:The instructor will walk around to thedifferent groups and supervise the disassembly answering any

questions the students may have

INSTRUCTOR NOTE

Perform the following practical application drainageand removal of the oil pan and pump.

(ON SLIDE #213)

TRANSITION: We just completed the practical application for removalof the oil pan and pump is there any other questions? If not I havesome questions foryou.

Thermal efficiency is the relationshipbetween actual heat energy stored within the fuel and the powerproduced in the engine (indicated horsepower). The thermal efficiencyfigure indicates how much of the potential energy contained in thefuel actually is

used by the engine to produce power and how muchenergy is lost through heat.

(ON SLIDE #216)

There is an extremely large amount of energy from the fuel that islost through heat in an internal combustion engine. This unused heatthat is produced while

the engine is producing power is of no valueto the engine and must be removed from it.

(1)

The heat is dissipated in the following ways.

INSTRUCTOR NOTE

Computer aided graphic intro fuel system 0.37minutes.

INSTRUCTOR NOTE

Computer aided graphic British thermal unit 0.17minutes.

QUIZ

(30min)

Hand out quiz for

diesel engine lubrication systemoperation and troubleshooting

quiz. Give the students20 minutes to complete and review it with thestudents after.

(a) The cooling system removes heat from the engine tocontrol engine operating temperature.

(b) A majorportion of the heat produced by the engineexits through the exhaust system.

(c) The engine radiates a portion of the heat to theatmosphere.

(d) A portion of this waste heat may be channeled tothe passenger compartment to heat it.

(e) The lubricating oil in the engine removes aportion of the waste heat.

(ON SLIDE #217)

(2)

In addition to energy lost through wasted heat, thereare the following inherent losses in the piston engine.

(a) Much energy is consumed when the piston mustcompress the mixture on the Compression stroke.

(b) Energy from the fuel is consumed to push theexhaust gases out of the cylinder.

oil).Although large, slow-speed diesel engines used in stationary andmarine applications will burn almost any grade of heavy oil, thesmaller, high-speed diesel engines used in most military equipmentrequire middle distillate diesel fuels. These fuelsmust meetexacting specification requirements to ensure proper engineperformance.

(ON SLIDE #220)

(1)

Cleanliness.

Fuel cleanliness is an importantcharacteristic of diesel fuel because the extremely close fit of theinjector parts can be damaged by particles.

(a) Dirt or sand particles in the fuel cause scoringof the injector parts, leading to poor performance.

(b) Moisture in the fuel can also damage of injectorparts when corrosion occurs.

(ON SLIDE #221)

(2)Stability.

Fuel stability is its capacity to resistchemical change caused by oxidation and heat. Good oxidationstability means that the fuel can be stored for long periods withoutformation of gum or sludge. Good thermal stability prevents theformation of carbon in hot parts such as fuel injectors. Carbondeposits disrupt the spray patterns and cause inefficient combustion.

(ON SLIDE #222)

(3)Cloud point.

The lowest temperature to which the fuelcan be subjected before it begins to cloud or form paraffin crystalsis the cloud point. This is very important if an item of equipment isoperated during cold weather. The paraffin or wax will clog fuelfilters and cause an engine to shutdown.

(ON SLIDE #223)

(4)

Viscosity.

The viscosity of a fluid is an indication ofits resistance to flow. This means that a fluid with a high viscosityis heavier than a fluid with a low viscosity. The viscosity of dieselfuel must be low enough to flow freely at its lowest operationaltemperature, yet high enough to provide lubrication to the movingparts of the finely machined injectors. The fuel must also besufficiently viscous so that leakage at the pump plungers anddribbling at the injectors will not occur. Viscosity will alsodetermine the size of the fuel droplets, which, in turn, govern theatomization and penetration qualities of the fuel injector spray.

(ON SLIDE #224)

(5)Sulfur.

All diesel fuels contain a certain amount ofsulfur, but high sulfur content is detrimental and will cause earlyengine failure. Sulfur does not burn except at extremely hightemperatures, so in many cases it simply accumulates in the engineoil and forms

The ignition quality of a fuel is itsability to ignite spontaneously under the conditions existing in theengine cylinder. The spontaneous-ignition point (flash point) of adiesel fuel is a function of the pressure, temperature, and time.

(ON SLIDE #226)

(a) The yardstick that is used to measure the ignitionquality of a diesel fuel is the cetane-number scale. The cetanenumber of a fuel is obtained by comparing it to the operation of areference fuel. The reference fuel is a mixture of alpha-methylnaphthalene, which has virtually no spontaneous-ignitionqualities, and pure cetane, which has what are considered to beperfect spontaneous-ignition qualities.

(b) The percentage of cetane is increased gradually inthe reference fuel until

the fuel matches the spontaneous-ignitionqualities of the fuel being tested. The cetane number then isestablished for the fuel being tested based on the percentage ofcetane present in the reference mixture.

(c) Cetane is not the same as octane. Octane is usedto rate gasoline and represents the ability of gasoline to resistrapid burning.

(ON SLIDE #227)

(7)

Knocking.

Diesel engines have a tendency to produce aknock that is noticeable particularly during times when the engine isunder a light load. This knocking occurs due to a condition known as“ignition delay” or “ignition lag”.

(1) When the power stroke begins, the first molecules offuel injected into the combustion chamber must first vaporize andsuperheat before ignition occurs.

(2) During this period, a quantity of unburned fuel buildsup in the combustion chamber. When ignition occurs, the pressureincrease

(3) The sudden ignition of the diesel fuel when injectedinto the combustion chamber causes a pressure wave.

(4) Increasing the compression ratio of a diesel enginewill decrease ignition lag and the tendency to knock. This isopposite of a gasoline engine, whose tendency to knock will increasewith an increase in compression ratio.

(5) Knocking in dieselengines is also affected by the typeof combustion chamber, airflow within the chamber, injector nozzletype, air and fuel temperature, and the cetane number of the fuel.

(ON SLIDE #228)

(ON SLIDE #229)

c.Fuel circuit components.

(1)

Fuel Tank.

The location of the fuel tank is dependenton utilizing an area that is protected from flying debris, shieldedfrom collision damage, and one that is not subject to bottoming. Afuel tank can be located just about anywhere in the equipment thatmeets these requirements.

(a)Construction.

Fuel tanks take many forms inmilitary equipment the most common material for fuel tanks is thinsheet metal. The walls of the tank are manufactured with ridges togive them strength. Internal baffles are sometimes installed in thetank to prevent the fuel from sloshing and to increase overallstrength.

(b)Filler Pipe.

A pipe is provided for filling thetank or cell that is designed to prevent fuel from being spilled intothe passenger, engine, or cargo compartment. The filler pipes used onmilitary vehicles are designed to allow their tanks to be filled at arate of at least 50 gallons per minute.

(c)Fuel return line.

The return line is normallylocated near the top of the fuel tank. Since diesel fuel is used tocool and lubricate the internal components of the system, returningfuel carries heat to the tank to be dissipated.

(d)Fuel supply line.

The supply line is normallylocated just above the bottom of the fuel tank. This location isideal to allow sediment to fall to the bottom of the tank without itbeing drawn into the fuel system.

INSTRUCTOR NOTE

Diesel fuel image.

(e)Drain plug.

A threaded drain-plug is usuallyprovided at the bottom of the tank for draining and cleaning.

(ON SLIDE #230)

(2)Fuel Tank Ventilation.

The most common methods ofventing a fueltank are either venting the fuel tank cap to theatmosphere, or providing a line to the fuel tank that vents at apoint that is high enough to prevent water from entering duringfording operations.The following are reasons why a fuel tank needsa good ventilation system:

(a)Air must be allowed to enter the tank as the fuelis pumped out. Without ventilation of the tank, the pressure in thetank would drop to the point where the fuel pump would not be able todraw any more fuel from it. In some cases, the

higher pressure aroundthe outside of the tank could cause it to collapse.

(b)

Temperature changes cause the fuel in the tank toexpand and contract. Absence of a ventilation system could causeexcessive or insufficient fuel line pressure.

(3)Fuel Gage

Provision.

A provision usually is made toinstall a fuel gage. This provision is normally in the form of aflanged hole.

(ON SLIDE #231)

d.Fuel filtration.

Thorough andcareful filtration is necessaryto keep diesel engines efficient. Diesel fuels are more viscous thangasoline and contain more gums and abrasive particles that may causepremature wear of injection components. The abrasives may consist ofmaterial that isdifficult to eliminate during refining, or they evenmay enter the tank during careless refueling. Whatever the source, itis imperative that means be provided to protect the system fromabrasives.

(ON SLIDE #232)

(1)Types.

Diesel engine designs usually

include twofilters (primary and secondary) in the fuel supply systems to protectthe closely fitted parts in the pumps and nozzles. Additionalfiltering elements are frequently installed in the system to provide